It may have been cyanide poisoning, if this is the case I am thinking of it was from sorghum after a drought:
Understanding Cyanide Poisoning-
A number of common plants may
accumulate large quantities of cya-
nogenic compounds. Sorghums and
related species readily accumulate
these compounds. These cyanogenic
compounds are in epidermal cells
(outer tissue) of the plant, while
the enzymes that enable cyanide
production are in the mesophyll
cells (leaf tissue).
Any event that causes the plant cell
to rupture, allowing the cyanogenic
compound and the enzyme to
combine, will produce cyanide.
Plant cells can be ruptured by cutting,
wilting, freezing, drought, crushing,
trampling, chewing or chopping.
Cyanide is a potent, rapidly acting
poison. Signs of cyanide poisoning
can occur within 15 to 20 minutes
to a few hours after animals consume
the toxic forage. Animals often are
found dead.
Remind me never to eat sorghum ever again...............